Aliphatic dicarboxylic acid chlorides, especially adipyl chloride, are used as starting materials for the manufacture of certain polyester foam materials, in accordance with the teaching of a U.S. application, Ser. No. 843,606, filed by T. A. DesMarais on Oct. 19, 1977. Specifically, that application (which is hereby incorporated herein by reference) teaches that straight-chain aliphatic compounds having 4 to 10 carbon atoms and acid chloride groups on each terminal end of the aliphatic chain may be combined with a guadrifunctional polyol, a propoxylated pentaerythritol cross linking agent and sodium carbonate to make a resilient polyester foam material which is useful in absorbent products such as catamenial tampons.
A principal method to synthesize the acid chlorides above-described is to react the corresponding carboxylic acid with phosphorus trichloride according to the following reaction: EQU 3R(COOH).sub.2 +2PCl.sub.3 .fwdarw.3R(COCl).sub.2 +2P(OH).sub.3
where R is an aliphatic chain. A more complete discussion of this reaction may be found in U.S. Pat. No. 1,936,739, issued to Townend on Nov. 28, 1933, which is hereby incorporated herein by reference. One significant problem with this synthetic route is that the resulting chlorides of dicarboxylic acids have a tendency to discolor upon standing. The reason for this discoloration and the nature of the discoloring material are not known to the inventors hereof, although the discolored matter is believed to be one or more degradation products of the dicarboxylic acid chloride. If discolored diacid chloride is used to make the polyester foam described above, the foam itself will be discolored. Since consumers dislike the resulting discolored foam materials, they are unsuitable for use in consumer products such as a tampon.
The Townend reference is the only prior art of which the inventors are aware. That reference teaches that it is desirable to treat an acid chloride formed by the phosphorus trichloride reaction by bubbling chlorine gas through the reaction mixture with the specific purpose of completing the reaction and eliminating any carboxylic acid residue from the resulting diacid chloride. That reference does not teach any way to prevent the discoloration of the acid chloride resulting from the reaction, and it specifically teaches that it is desirable to eliminate the carboxylic acid starting material from the produce of the reaction.
Accordingly, it is an object of this invention to clarify or to preserve the clarity of an aliphatic dicarboxylic acid chloride, and it is a further object of this invention to produce a dicarboxylic acid chloride starting material which may be used in the manufacture of substantially colorless polyester foams according to the process described in the DesMarais application cited on page 2 hereof.